Umarbajwa - CraftedSignal Threat Feedhttps://feed.craftedsignal.io/vendors/umarbajwa/Trending threats, MITRE ATT&CK coverage, and detection metadata. Fed continuously.Hugoenhello@craftedsignal.iohello@craftedsignal.ioSat, 01 Aug 2026 09:50:02 +0000Stored Cross-Site Scripting in MailChimp Subscribe Form Plugin for WordPresshttps://feed.craftedsignal.io/briefs/2026-08-mailchimp-xss/Sat, 01 Aug 2026 09:50:02 +0000hello@craftedsignal.iohttps://feed.craftedsignal.io/briefs/2026-08-mailchimp-xss/An unauthenticated stored XSS vulnerability in the MailChimp Subscribe Form, Optin Builder, PopUp Builder, Form Builder WordPress plugin (up to version 4.3.3) allows attackers to inject arbitrary web scripts into form fields.The 'MailChimp Subscribe Form, Optin Builder, PopUp Builder, Form Builder' plugin for WordPress, developed by umarbajwa, contains a high-severity stored Cross-Site Scripting (XSS) vulnerability, tracked as CVE-2026-15052. The flaw exists in all versions up to and including 4.3.3 and stems from improper input sanitization and output escaping within the plugin's form handling logic. An unauthenticated attacker can supply malicious JavaScript payloads via form fields. These scripts are subsequently stored in the database and executed in the browser of any user who views the page where the form results or data are rendered. This vulnerability poses a significant risk to site administrators and users, as it could facilitate session hijacking, unauthorized actions on behalf of users, or the redirection of visitors to malicious domains.

Attack Chain

  1. Attacker identifies a WordPress site utilizing the vulnerable MailChimp Subscribe Form, Optin Builder, PopUp Builder, Form Builder plugin (version 4.3.3 or earlier).
  2. Attacker crafts a malicious JavaScript payload intended for execution in a victim's browser context.
  3. Attacker submits the crafted payload through a public-facing input field provided by the plugin.
  4. The plugin fails to sanitize the input before committing the data to the WordPress database.
  5. The plugin serves the stored, unsanitized input to users (e.g., in an administrative dashboard or public submission view).
  6. The victim's browser interprets the stored data as executable script rather than plain text.
  7. The attacker's script executes in the context of the victim's session, potentially allowing unauthorized data access or session theft.

Impact

Successful exploitation of CVE-2026-15052 allows unauthenticated attackers to execute arbitrary JavaScript within the context of the affected WordPress site. This can lead to account takeover if an administrator views the injected content, unauthorized modifications to site content, or the persistent redirection of site visitors to external malicious sites. Given the prevalence of WordPress, this vulnerability impacts any organization currently running versions 4.3.3 or lower of this specific plugin.

Recommendation

  • Update the 'MailChimp Subscribe Form, Optin Builder, PopUp Builder, Form Builder' plugin to a version greater than 4.3.3 immediately.
  • If an update is not immediately available, disable the plugin to prevent further exploitation until a patch is applied.
  • Review WordPress access logs for anomalous POST requests to the plugin's form submission endpoints containing script-like characters (e.g., <script>, onload=, onerror=).
  • Implement a strong Content Security Policy (CSP) to mitigate the impact of XSS attacks by restricting the sources from which scripts can be executed.
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